Doctors may be giving the wrong doses of life-saving adrenaline because of confusing labelling, a study suggests.
Adrenaline injections are given after severe allergic reactions
Adrenaline, which is used to treat emergencies such as asthma attacks, is stored in vials with the amount often expressed as a ratio as well as a dose.
The ratio requires arithmetic to work out how much drug to administer.
In a test, only two of 14 doctors using the ratio were able to give the correct amount, researchers writing in the Annals of Internal Medicine said.
They also took about 1.5 minutes longer than doctors using the dose information to give the injection to the medical mannequin.
"The findings might be different if the doctors had to treat a real person," said Dr Daniel Wheeler, who carried out the research at the University of Cambridge. "In reality the labels have ratios and doses, not one or the other.
"However this does give us insight into the problem and a fairly easy solution - expressing drug concentrations exclusively as doses - we believe would improve patient safety."
There have long been concerns about the administration of adrenaline, with studies also raising concerns about the use of pre-loaded injection "pens".
Adrenaline shots are given if a patient has had a serious faint, has choked, or had a severe asthmatic reaction.